The invention relates generally to the field of myography and is more particularly directed to apparatus for measuring characteristics of the lip and tongue muscles.
Myography is concerned with the measurement of contractions and relaxations of the skeletal muscles. In the diagnosis and treatment of various disorders involving the face and mouth, it is often desirable to determine the strength of the face and mouth muscles. Such determinations may be useful, for example, in assessing and treating certain speech disorders, in assessing the need for physical therapy for stroke victims, and for tracking progress in recovery from strokes or other injury to the mouth or face. Measurement of orofacial muscle strength may also be useful in connection with oral surgery, particularly where the musculature is to be cut. Measurements prior and post operation, for example, can aid in determining an appropriate course of isometric exercise or other physical therapy.
Although muscle strength measurements are recognized as a useful modality in diagnosis and assessment, in practice instrumentation for making direct measurements of orofacial muscle strength is not widely used. In one recent attempt to provide a direct-measurement orofacial instrument, for example, the patient "bites down" on a mechanical probe with the lips or pushes against the probe with the tongue and the instrument measures the strain induced in the probe with a strain gauge. From the strain gauge measurement the instrument gives a reading of the mechanical force of the patient's bite or push.
This type of instrument is subject to a number of drawbacks typical of the problems encountered with the direct measurement technique. It is difficult to obtain reproducibility of results because the measurement probes are sensitive to the precise positioning of the probe in the patient's mouth, that is, to the precise location at which the patient applies the force. In addition, a variety of different probe sizes are needed for different mouth sizes, and it then becomes more difficult to maintain a common calibration among the varied probe sizes.
In view of the uncertainty of direct strength measurements by known techniques, many practitioners either expect only rough, primarily subjective, estimates of muscle strength and consequently do not rely much on the strength-measurement modality, or they avoid direct force measurements altogether and instead use other techniques for monitoring muscle activity such as electromyographic measurements, which measure electrical response of the muscles.